How to Register Open Generics in .Net Core DI

In this article, we will discuss how to register open generics in .Net Core Di. Dependency injection is a popular design pattern used in software development to create loosely coupled applications. .Net Core Dependency Injection (DI) is a powerful feature that enables developers to implement DI in their applications easily. One of the key benefits of DI is that it allows for flexible and easy-to-maintain code. This is achieved by separating the concerns of object creation from object usage. .NET Core supports a wide range of registration options, including open generics. Open generics allow you to register a generic type without specifying the type parameters, which can be useful when you want to provide a more generic service. In simple terms, it enables you to define a generic type without specifying its type parameters, allowing it to be used with different types at runtime. Open Generics in .NET Core Dependency Injection provides a powerful and flexible way to register and resolve generic types, making it easier to work with complex applications that require dynamic type resolution.

What is Open Generics?

In .NET Core, a generic type is a class, interface, or method that can work with different types of data. An open generic is a generic type that has at least one unspecified type parameter. For example, List<> is an open generic because it has an unspecified type parameter. On the other hand, List<int> is a closed generic because it has a specified type parameter.

Open generics are useful because they allow you to create generic components that can work with a variety of different types. For example, you could create a Repository<T> class that can work with any type of object, rather than creating a separate repository class for each type. Open Generics are implemented using the typeof(T) syntax, where T is a generic type parameter that represents the type to be resolved at runtime.

Note: Note that when you use an open generic type in this way, .NET Core will automatically resolve the closed generic type when it is requested by the application. So if you have multiple implementations of IRepository<>, the correct implementation will be injected based on the generic type arguments that are used.

Registering Open Generics in .NET Core:

To register open generics in .NET Core Dependency Injection, you can follow these steps:

// Define the open generic interface

public interface IRepository<T> where T : class


    void Add(T entity);


// Define the open generic implementation

public class Repository<T> : IRepository<T> where T : class


    public void Add(T entity)


        // Add entity to database



// Register the open generic interface and implementation in Startup.cs

public void ConfigureServices(IServiceCollection services)


    services.AddTransient(typeof(IRepository<>), typeof(Repository<>));


In the above example, IRepository<T> is the open generic interface and Repository<T> is the open generic implementation. By calling services.AddTransient(typeof(IRepository<>), typeof(Repository<>)), you are telling the dependency injection container to resolve any instance of IRepository<T> by creating an instance of Repository<T>.

Note: Note that you need to use typeof(IRepository<>) and typeof(Repository<>) instead of the concrete types IRepository<T> and Repository<T> to register the open generics.

To register open generics in .NET Core, we use the AddScoped, AddTransient, or AddSingleton method of the IServiceCollection interface. You need to use the non-generic overload of the Add[Lifetime] method, and use the typeof keyword to specify your open generic interface and implementation. Here’s an example: These methods take two parameters: the open generic type and the implementation type.

 services.AddTransient(typeof(IRepository<>), typeof(Repository<>));

In this example, we're registering an open generic IRepository<> and its implementation Repository<>. The AddTransient method specifies that a new instance of Repository<> should be created each time IRepository<> is requested.

If you're not familiar with the ServiceCollection class, it's the central DI container in .NET Core. You can access it in your application's Startup class using the ConfigureServices method.

Methods to register Open generics in .Net Core:

In addition to the AddTransient method, there are two other methods you can use to register open generics:

AddScoped: Specifies that a new instance of the registered type should be created once per scope (e.g. per HTTP request in a web application).

AddSingleton: Specifies that a single instance of the registered type should be created and reused for the lifetime of the application.

Here's an example of how to register an open generic using AddScoped:

services.AddScoped(typeof(IRepository<>), typeof(Repository<>));

And here's an example of how to register an open generic using AddSingleton:

services.AddSingleton(typeof(IRepository<>), typeof(Repository<>));

In addition to registering open generics with a single type parameter, you can also register open generics with multiple type parameters. Here's an example:

services.AddTransient(typeof(IRepository<,>), typeof(Repository<,>));

Why should use open generics Di:

  • To register and resolve generic types in.NET Core Dependency Injection, use Open Generics. By specifying dependencies on generic types, which can be instantiated with specified type parameters at runtime, they enable developers to build more general and reusable code. This offers a solution to lessen duplication of code and improve maintainability.

  • Moreover, registering dependencies in the DI container can be made simpler by using Open Generics. Rather than registering each unique implementation of a generic interface or abstract class separately, you can register the open generic type with the container and it will resolve the correct implementation based on the type argument provided at runtime.

  • Open Generics can also make it easier to extend and modify code in the future. By using generic types and interfaces, you can write code that is more flexible and adaptable to changes in requirements or new use cases.

  • In general, Open Generics in.NET Core Dependency Injection can promote maintainability and flexibility while promoting code reuse and reducing duplication.

  • With Open Generics, developers can register a generic type in the DI container and provide a concrete implementation when it is needed. This means that developers can write code that is more flexible and can handle a wider range of scenarios.

  • Open Generics can also help to simplify code and reduce the amount of boilerplate code that needs to be written. It can also make code more testable by allowing developers to inject dependencies that are more easily mocked.


In this article, we have explored how to register open generics in .Net Core DI. We started by defining an open generic interface and its implementation, We then registered the open generics. Open Generics is an essential feature of .NET Core DI that can help developers write more flexible, reusable, and testable code. It is a valuable tool that can help developers to create high-quality software that is easy to maintain and extend over time.

Hope you enjoyed reading this article and found it useful. Please share your thoughts and recommendations in the comment section below.

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